1. Field of the Invention
The present invention generally relates to wheels that are equipped with a decorative wheel cover. More specifically, this invention relates to an apparatus and related method for adhesively securing a wheel cover to a wheel in a manner that results in a more economical, yet complete volumetric fill of adhesive therebetween to enhance sound deadening characteristics, and that results in a faster cure time of the adhesive and cycle time of the assembly process when compared to the prior art.
2. Description of the Related Art
Various methods for adhesively attaching two components together to make an assembly have been well known for a long time. More specifically, many types of decorative wheel covers are widely known to be adhesively attached to an underlying wheel to economically enhance the aesthetic appearance of many different types of automobile wheels. A classic example of a vehicle wheel construction having an adhesively attached wheel cover is U.S. Pat. No. 3,669,501 to Derleth.
Derleth discloses an annular-shaped overlay composed of a thin plastic cover formed from acrylonitrile-butadiene-styrene (ABS) mounted to a wheel spider. The overlay is configured to have variations in contours in a direction transverse to the axis of the wheel which exceed the variations in the rim and/or disc contour of the wheel, which variations would be extremely difficult and expensive, if not impossible, to stamp or draw in the disc of the wheel. During assembly, an adhesive foamable polyurethane is coated on the wheel, and the cover is then quickly clamped to the wheel before the polyurethane begins to foam. As such, the void between the wheel and cover is filled with the polyurethane foam, and any excess polyurethane foam formed around the bolt holes or at the periphery of the assembly must be trimmed. Thus, the polyurethane foam serves to permanently adhere the cover to the wheel.
Derleth teaches that the polyurethane foam adhesive provides a low-density, semi-resilient reinforcement for the thin gauge plastic cover while also providing sound insulation for tire and wind noise. However, it is understood by those skilled in the art that another reason for spacing the overlay's cover from the wheel surface is to avoid the deleterious effects of heat generated by the wheel and brake, which would otherwise distort the plastic cover and delaminate any surface treatment, i.e. paint, plating, etc., applied thereto. Further, the polyurethane foam adhesive completely breaks down at high temperatures experienced under certain actual road conditions. This is particularly true in the immediate region of the wheel hub where temperatures tend to be much higher than in the remainder of the wheel. While the polyurethane foam adhesive taught by Derleth has an insulating effect, the thermal barrier provided by the foam adhesive is inferior to air. Also, the manner in which the foam adhesive is formed in situ on the wheel does not readily permit limiting the degree to which the foam adhesive fills the cavity.
One obvious shortcoming of the process disclosed by Derleth is that the composite wheel must be imperforate, except for the small bolt openings necessary for attaching the wheel to a vehicle. It is understood by those skilled in the art that it is necessary to avoid the deleterious effects of heat generated by the wheel and brake that cause the ABS plastic overlay to distort, cause delamination of any surface treatment, i.e. paint, plating, etc., and further cause the foam adhesive to degrade, distort and eventually melt. Further problems with urethane formed wheels surfaced in use. These wheels were very heavy due to the high density of the foam and variation in localized density during the manufacturing phase resulted in severe wheel imbalances and costly assemblies.
Turbine openings are a necessary element in today's wheel systems in providing proper cooling to the brake system, not to mention the aesthetics of endless configurations of turbine openings that add individuality and style to a vehicle. Any opening in the wheel or overlay using the process disclosed in Derleth is a pathway for the foam mixture to escape when it begins to foam and/or cure. Larger openings, such as turbine openings, would not be possible using the Derleth process without additional structure to seal the openings to prevent the foaming material from escaping. Therefore, a drawback of the process according to Derleth is that excess foam mixture is required to ensure that the cavity between the cover and the wheel is completely filled after the material vents out through the bolt openings. The process disclosed by Derleth requires any substantial opening in the wheel be plugged or sealed with a sleeve to prevent foam leakage. For example, if the wheel hub was left unsealed it would provide a path for some of the foam to escape, and the security of the cover could be jeopardized. Further, all of the excess foam must be manually removed, which adds significant labor cost to the process.
The method according to Derleth has been known since the early 1970's and due to its many disadvantages has yet to realize practical applications and commercial success. The process cannot accommodate the application temperature requirements, the need for lighter weight components, and degradation of the urethane adhesive over time, as well as the need for turbine openings in the outboard face of the wheel. Further, the process is extremely costly due to the labor intensive trimming operations, difficult process control, and potential environmental, health and safety concerns.
Another example of an adhesively attached wheel cover is taught in U.S. Pat. No. 4,416,926 to Maglio which discloses adhering a wheel cover to a wheel with a resin matrix containing hollow microspheres to form a structural syntactic foam and reduce the density of the resin to result in a lightweight product. Similar to the teachings of Derleth, the wheel cover taught by Maglio is also axially spaced away from the wheel to avoid the wheel's potentially high temperatures, particularly near the center of the wheel. Unfortunately, however, the Maglio disclosure does not at all teach one skilled in the art how to introduce the hollow microspheres into the resin to achieve the syntactic foam. Furthermore, Maglio does not teach a process, or at what point in the process, wherein the microspheres are introduced and what effect the microspheres have on the fill volume or cure rate of the foam.
U.S. Pat. No. 5,753,747 to Oien, however, does teach just such a process. Oien teaches a method of using a hot-melt adhesive containing a particulate filler to fill cavities in a substrate wherein the particulate filler improves the cure time of the adhesive. Oien discloses a method of mixing, among many other ingredients, the hot-melt adhesive with a quantity of hollow inorganic microspheres to form a cellular hot-melt adhesive composition. Again, it is submitted that such a process is unnecessarily complicated as evidenced by the many required chemical components and the lengthy and intricate recipe disclosed in Oien. Furthermore, use of hot-melt adhesive is generally not acceptable for use with a wheel assembly near the hub of the wheel, where braking heat can easily destroy the adhesive properties thereof.
U.S. Pat. No. 5,188,428 to Carter, III teaches a decorative wheel having a unique wheel cover retention system for attaching to an ordinary underlying automotive wheel in a manner that more closely duplicates the appearance of a custom wheel. Carter, III discloses a specially configured plastic wheel cover that includes a deeply contoured body portion and a narrow outer rim portion. The retention system is disposed between the wheel cover and the wheel and includes two mating rings arranged concentrically, the first of which attaches to the back of the wheel cover, the second of which secures to the automotive wheel. The second ring is permanently attached to the automotive wheel with an adhesive that bonds the second ring to an annular wall of the wheel in a manner that provides a secure bond between the dissimilar materials. The adhesive is a one-part silicone rubber adhesive that sets at room temperature but does not harden and, thus, remains elastic and flexible.
A further example of bonding an overlay to a wheel is taught by Beam in U.S. Pat. Nos. 5,368,370 and 5,461,779. Beam teaches an ornamental appliqué formed on a uniform thickness of stainless steel sheet stock that requires attachment to the wheel by the use of a full surface curable adhesive uniformly deposited between the stainless steel cover and a mechanical locking arrangement. The mechanical locking arrangement consists of an undercut in the rim of the wheel into which the cover nests and a hole in the wheel aligned with a hole in the applique wherein a lug stud is permanently attached to create a mechanical lock that, according to Beam's teachings, compresses the full surface uniform layer of curable adhesive to hold the applique in place until the adhesive cures.
Beam's teachings present several problems. The mating of the stainless steel and the steel wheel at the rim area results in a galvanic action occurring that visibly is unacceptable in the marketplace. Further, at the hub portion of the wheel, the high temperatures experienced under certain driving or testing conditions may detrimentally affect the full surface uniform layer of curable adhesive while the cost of using a full surface curable adhesive is prohibitively expensive and wasteful since there is no need for a full surface uniform layer of adhesive to hold the overlay to the wheel. Further, a full surface uniform layer of curable adhesive also detrimentally affects the balancing considerations of the wheel and overlay assembly.
To avoid some of the problems of Beam, U.S. Pat. No. 5,597,213 to Chase, assigned to the assignee hereof, teaches the use of an intermediate positive fixing element for temporarily positioning and securing an overlay to a wheel during an interval in which a selectively positioned or applied adhesive required to permanently adhere the overlay to the wheel is allowed to cure. A temporary hot melt adhesive is combined with the use of a high strength, slow-curing adhesive, both of which are selectively placed between the overlay and the wheel to alleviate concerns of squeaks and rattles as well as to improve the overall manufacturability, performance and consumer-perceived quality of the resulting wheel assembly. The hot melt adhesive is capable of creating a bond almost instantly, but is ill suited for securing the overlay to the outboard surface of the wheel over its service life, that is, once the wheel is installed and in use on an automobile. Therefore, the hot-melt adhesive is characterized as being suitable only for temporarily securing the overlay to the outboard surface of the wheel during the assembly of the overlay and wheel and while the high strength, slow-curing adhesive is curing. Advantageously, such use comes during a critical period when the overlay is susceptible to movement relative to the wheel. Accordingly, while the hot melt adhesive is not suitable for permanently securing the overlay to the wheel, the hot melt adhesive is readily capable of positively maintaining the position of the overlay on the outboard surface of the wheel during the period in which the high strength, slow curing adhesive is curing.
Chase discloses selectively depositing the adhesive beads in parallel, but separated lines of adhesive rather than a solid layer to create voids so as to reduce the amount of curing time of the adhesive and thereby reduce manufacturing time and costs. As such, air between the lines of adhesives is captured between the overlay and the wheel to assist in curing the adhesive. Further curing for certain adhesives is significantly reduced by exposure to moisture laden air. In such cases high humidity air is introduced into the assembly process and the technique of selective application of the adhesive can be utilized to establish voids between lines of adhesive that serve to entrap moisture laden air further enhancing cure times and reducing overall costs of the manufacturing process. The requirement of an intermediate positive fixing element, or temporary adhesive, not only adds costs and complexity to the overlay but requires careful handling and special packaging, all adding to the overall cost of the wheel assembly. Additionally, the need to use redundant beads of adhesive adds to process time, material cost, and weight of the wheel assembly.
Similarly, U.S. Pat. No. 5,845,973 to Chase is a continuation of the Chase '213 method and apparatus. Chase '973 is a method for compensating for axial tolerance variations defining a gap between an overlay and a wheel. The dimension of the gap varies according to hi-lo conditions of various axial dimensions of each of the overlay and the wheel. Therefore, sufficient adhesive is placed between the overlay and the wheel to accommodate these variations in the gap. Since the gap is said to vary as much as 0.25 inches, it is preferred that a foam adhesive is used at the center of the wheel to minimize excessive squeeze out of the adhesive. Unfortunately, however, structural foam adhesives, such as disclosed in Derleth and Chase, are relatively expensive compared to sealant bead alternatives such as silicone RTV, and also present costly processing techniques in order to seal the assembly so that the expanding foam does not squeeze out and create a mess.
U.S. Pat. No. 5,636,906 to Chase, also owned by the assignee hereof, teaches a decorative overlay to enhance the aesthetic appearance of an automotive wheel. The overlay described in the preferred embodiment is a metal-plated plastic panel that is adhesively attached to the outboard surface of the wheel disc and may radially extend to the flange lip of the rim flange so as to cover the outboard surface in the rim flange area of the wheel. The overlay provides a pleasing aesthetic effect to the wheel. The overlay covers most of the wheel's outboard surface but does not extend radially outward to cover the edge or flange lip of the rim flange of the wheel. The base material composition and metal plating of the overlay permit the exterior surface of the overlay to be closely contoured to the outboard surface of the wheel, namely, the disc of the wheel and a major portion or all of the rim flange of the wheel. Further, the overlay resists delamination of the metal plating due to heat.
Maloney et al., U.S. Pat. No. 5,435,631, is directed to the problems associated with the retention of wheel covers to a wheel. Maloney et al. teach a wheel cover retention system, wherein the outboard tire bead seat retaining flange or rim flange of the wheel includes a groove as taught in Beam for securing the wheel cover to the wheel. Maloney et al. further teach that an outboard tire bead seat retaining flange of a wheel includes a unique construction for securing the wheel cover to the wheel. The outboard tire bead seat retaining flange includes an outer surface having a circumferential, radially inwardly facing groove formed therein. A relatively thin wheel cover having an outer annular lip extends into the groove in the outboard surface of the wheel. The groove functions, in part, to hide a peripheral edge of the cover. With respect to the method used for assembling the cover to the wheel, Maloney et al. is completely devoid of any specific teaching with respect to the relationship of the cover relative to the outboard surface of the wheel with the exception that the outer annular lip extends into the groove. Other than this specific teaching, Maloney et al. teach that the wheel cover is preferably formed from stainless steel and is prefabricated to generally match the particular configuration of the outboard facing surface of the disc.
Maloney et al. disclose that an adhesive, such as a two-part epoxy, is used to permanently secure the wheel cover to the wheel. The adhesive is preferably applied on the outboard face of the wheel disc in a predetermined pattern consisting of an inner circle, an outer circle, and angled radial lines. Such a pattern is selected so that when the wheel cover is installed on the wheel disc, a smearing of the adhesive occurs over substantially the entire outboard face of the wheel disc.
Unfortunately, the patterns of adhesive as disclosed in the Chase patents and Maloney et al. have several well known drawbacks. First, such high-strength adhesives are costly, take an exceedingly long time to cure, and may require application of heat to cure properly. The adhesive usually takes at least 24 hours to cure sufficiently before the wheel assembly can be shipped without possibility of wheel cover separation during transit or at the assembly plant. Any reduction in this initial cure time is desirable to reduce the turnaround time in supplying an assembly plant with finished wheel assemblies, and thereby reduce the amount of work-in-process (WIP) and inventory costs related thereto. Since wheels must be available to the wheel cover manufacturer for producing the finished wheel assemblies, the wheel cover manufacturer's process is reliant upon the continuous availability of wheels from the wheel manufacturer. From time to time a shortage of wheels occurs, thus causing a shortage of finished wheel assemblies available to the assembly plant. As the supply of wheels from the wheel manufacturer becomes restored, the pressure to quickly supply finished wheel assemblies to the vehicle assembly plant is enormous. It is therefore desirable to reduce the throughput time in converting the wheels and wheel covers into sufficiently cured finished wheel assemblies. Currently, the excessive 24 hour cure time has too much potential to result in a temporary line shutdown at a customer assembly plant. Additionally, the excessively long initial cure time unfortunately necessitates temporary securing features, adhesives, or slave tools.
Second, use of such high-strength adhesives ordinarily results in a substantial air gap in multiple areas between the wheel cover and wheel. The existence of such an air gap has generated a concern among wheel engineers relating to the sound deadening abilities of the adhesive between the wheel and the wheel cover. Since automobile wheels experience harsh environments during their useful life, it has often been the practice of wheel engineers to rap on the wheel cover attached to the wheel to gauge the “soundness” of the wheel assembly. Unfortunately, however, the inclusion of the air gap between the wheel cover and the wheel tends to yield a relatively loud and undesirable hollow sound when rapped upon.
Finally, application of such high-strength adhesives usually results in a relatively thin bead that is often inadequate to fill the gap between the wheel cover and wheel in certain areas and thereby necessitates a close relationship therebetween. Accordingly, if a wheel designer wishes to space the wheel cover inboard surface a greater distance from the wheel outboard surface, a structural foam adhesive needs to be used instead of the bead of sealant or adhesive.
Methods, systems, and articles involving applying beads of sealant or adhesive have been well known for quite some time. For example, U.S. Pat. No. 4,059,714 to Scholl teaches a method of bonding using a hot melt thermoplastic adhesive foam. Unlike the adhesive foam described in Derleth and Chase, the adhesive foam of Scholl is akin to a thermoplastic paste that is foamed by mixing an inert gas therewith to produce the foam. While the adhesive is in a liquid state the adhesive/gas mixture is pressurized to force the gas into solution with the adhesive. When the pressurized adhesive/gas mixture is dispensed from a nozzle at atmospheric pressure, the gas comes out of solution and becomes entrapped within the adhesive to form a closed cell hot-melt adhesive foam.
Similarly, U.S. Pat. No. 5,382,397 to Turner, Jr. teaches a method of applying a closed cell foam seal to an automotive body seam. Turner, Jr. discloses the method having the following steps: supplying a polymeric sealant of thermoplastic, thermoset, or plastisol composition; mixing the sealant with an inert gas; pressurizing the sealant and gas mixture to drive the gas into solution within the sealant; maintaining the gas in solution within the sealant; dispensing the sealant/gas mixture in the form of a foamed bead into an automobile body seam; controlling the foamed bead to a desired width and amount; and curing the foamed bead to seal the automobile body against intrusion of moisture, dust, and noise.
Finally, methods for applying foamed-in-place gaskets have been generally well known. For example, U.S. Pat. No. 4,834,824 to Tiedeck teaches a method of forming a foamed-in-place gasket for a workpiece to be mounted on a support member, wherein a continuous sealant bead is applied upon a coated release board and transferred to the workpiece. Similarly, U.S. Pat. No. 5,324,470 to Comert et al. teaches a method of forming a gasket in place on a surface of a pipe flange from a non-foamed bead of a moisture curable material. Unfortunately, none of the last four prior art references described above identify the peculiar problems associated with securing a wheel cover to a wheel, nor do they suggest any particular solutions thereto.
From the above, it can be appreciated that adhesive attachment systems of the prior art are not fully optimized to solve the peculiar problems of effectively attaching a wheel cover to a wheel for use in a harsh environment for the life of the vehicle. Therefore, what is needed is an improved method of securing a wheel cover to a wheel that is economical to produce, requires significantly less cure time of a bead of adhesive used therein, and that more effectively and efficiently fills the gap between the wheel and wheel cover so as to provide improved sound deadening characteristics over a conventional bead of adhesive.